1. Field of the Invention
This invention relates to the digitization of an analogue signal mechanical gauge. Particularly, this invention relates to the digitization of an analogue signal from a mechanical pressure gauge. More particularly, this invention is related to the digitization of an analogue signal from a mechanical pressure gauge that uses a Bourdon tube.
2. Description of the Related Art
The measure of pressure is often a key parameter when dealing with gases. Pressure gauges have been used on cylinders of compressed industrial gas for a long time and many different types of technologies are currently available in the market. Over the past couple of decades gauges have been introduced in the head of cylinders to provide a measurement of the pressure inside the cylinder or at the outlet of the cylinder. Pressure reducers have also had integrated gauges for some time.
Perhaps the most common type of gauge is the mechanical gauge. This type of technology has been used for a long time, and is continuously being improved upon. Well known systems, such as Bourdon tube, are very often used to measure both high and low pressure. These types of gauges typically are very low in cost, perhaps on the order of $2 to $4 each. Despite the relatively low cost, this type of gauge still offers information that is visual, the precision of which relies on the accuracy of the viewer.
However, a large part of the market routinely relies on electronic gauges. These gauges rely on Wheatstone Bridge principle which includes a measuring cell. Such cells are typically based on piezoelectric devices, or similar technology, which has physical properties that are modified by the pressure and then measured by the Wheatstone Bridge. Analogous examples of such systems may be found in U.S. Pat. No. 4,643,030, wherein a set of strain gauges are affixed to an automotive torque wrench, and U.S. Pat. No. 5,065,631, wherein a tube containing strain gauges is affixed to a metal structure.
These types of electronic gauges are very precise, the sensing cell and the Wheatstone Bridge packaged to fit a high pressure application may typically cost from $7 to $15 each for the simplest technologies. The measurement of the pressure of gas inside of a cylinder is often designed to use pressure reducers, a screen and all the necessary electronics, as well as the necessary batteries. Packaged technologies that apply to the measurement of cylinders of industrial gas may range from $30 to $200.
Some manufacturers have moved to intermediate technologies, that fill the gap between those two extremes. One of the most common solutions has been to use a rheostat mechanically linked to the axe of the needle of a mechanical gauge. Such a solution is cheaper than a digital solution, however it is usually necessary to significantly modify the design of the gauge itself. Others such as Mija, a Connecticut based company which manufacture sensors for fire extinguishers, has developed a system that fits inside the gauge and features devices to detect the relative position of the needle of the mechanical gauge.
A need exists within the industry, for an inexpensive, yet reliable and accurate means to retrofit existing mechanical pressure gauges in such a way as to produce a digital signal.